1. Field of the Invention
The present invention relates to a magnetic recording medium comprising a magnetic recording layer on a non-magnetic support member and more particularly, it is concerned with a magnetic recording medium having an improved surface property.
2. Description of the Prior Art
In the recent video tapes, recording wavelength of 2 microns or less, in particular, about 1.5 microns have often been used.
In order to obtain a good image quality, it has been desired to increase the S/N ratio by increasing the signal output (S) and decreasing the noise level (N). As a method for decreasing the noise level by improving a magnetic layer, there have been made various proposals, for example, comprising using dispersing machines, main binders or dispersing agents, which serve to increase the dispersibility of magnetic substances, or comprising removing materials decreasing the dispersibility of magnetic substances, such as synthetic rubbers. In addition, as an effective method for decreasing the noise level, it has also been proposed to use a base having a smooth surface without changing the magnetic coating composition and the operations for preparing and applying the coating composition. The surface smoothness of a base is closely related with that of a coating film. That is to say, a good smoothness base gives a smooth coating surface and rough surface base give a rough coating surface. On the other hand, the width of a head track has lately been narrowed to about 50 to 70 microns from 100 to 150 microns in the prior art and even small dusts thus ten to be detected as drop outs, so that drop outs be largely increased at a base surface roughness of 0.33 micron or less. Furthermore, in a magnetic recording medium using a base with a surface smoothness of 0.33 micron or less, the base surface opposite to the magnetic layer is more readily scraped during running in a VTR than that using a base with a rough surface and transferred to the magnetic layer, resulting in increase of drop outs.